Polymeric diffusion matrix

ABSTRACT

A polymeric diffusion matrix is provided comprising from about 2 to about 60% glycerol, from about 2 to about 15% polyvinylalcohol, from about 2 to about 10% water soluble polymer with hydration sites which in combination with the remaining ingredients yields a matrix capable of sustained release of a drug dispersed therein, and the balance water, the percentages being by weight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 258,456,filed Apr. 28, 1981, which in turn is a continuation of application Ser.No. 109,242, filed Jan. 3, 1980 and now abandoned, which in turn is acontinuation-in-part of application Ser. No. 47,084, filed June 11, 1979and now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 2,565 filed Jan. 11, 1979 now abandoned.

SUMMARY OF THE INVENTION

A polymeric diffusion matrix is provided comprising from about 2 toabout 60% glycerol, from about 2 to about 15% polyvinylalcohol, fromabout 2 to about 10% water soluble polymer with hydration sites which incombination with the remaining ingredients yields a matrix capable ofsustained release of a drug dispersed therein, and the balance water,the percentages being by weight. Preferably, said water soluble polymeris polyvinylpyrrolidone, agar, agarose or a water soluble cellulosederivative, a preferred embodiment being polyvinylpyrrolidone. Thepolyvinylalcohol preferably has a molecular weight of from about 100,000to about 150,000 and the polyvinylpyrrolidone preferably has a molecularweight of from about 20,000 to about 60,000.

In a preferred embodiment, a polymeric diffusion matrix suitable for thetransdermal delivery of a drug is provided comprising from about 2 toabout 60% glycerol, from about 2 to about 15% polyvinylalcohol, fromabout 2 to about 10% water soluble polymer with hydration sites which incombination with the remaining ingredients yields a matrix capable ofsustained release of a drug dispersed therein, at least one drugsuitable for transdermal delivery to a patient and the balance water,the percentages being by weight. Preferably, said water soluble polymeris polyvinylpyrrolidone, agar, agarose or a water soluble cellulosederivative, a preferred embodiment being polyvinylpyrrolidone. Thepolyvinylalcohol preferably has a molecular weight of from about 100,000to about 150,000 and the polyvinylpyrrolidone preferably has a molecularweight of from about 20,000 to about 60,000. The polyvinylalcoholpreferably has a molecular weight of from about 100,000 to about150,000.

In a separate embodiment, a polymeric diffusion matrix in cured formsuitable for providing protection to a burned or wounded patient isprovided which comprises in the cured state from about 2 to about 55%glycerol, from about 4 to about 30% polyvinylalcohol, from about 2 toabout 20% water soluble polymer with hydration sites which incombination with the remaining ingredients yields a matrix capable ofsustained release of a drug dispersed therein, and the balance water,the percentages being by weight. Preferably said water soluble polymeris polyvinylpyrrolidone, agar, agarose, and a water soluble cellulosederivative, the preferred embodiment being polyvinylpyrrolidone. Thepolyvinylalcohol preferably has a molecular weight of from about 100,000to about 150,000 and the polyvinylpyrrolidone preferably has a molecularweight of from about 20,000 to about 60,000. Preferably the ratio ofpolyvinylalcohol to polyvinylpyrrolidone is from about 2:1 to about 3:2.At least one topical drug may be incorporated in said matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of a bandage having incorporated therein thedrug-containing polymeric diffusion matrix of the present invention; and

FIG. 2 illustrates a cross-sectional view along line 2--2' in FIG. 1

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, a polymeric diffusion matrix isprovided comprising, on a weight basis, from about 2 to about 60%glycerol, from about 2 to about 15% polyvinylalcohol, from about 2 toabout 10% water soluble polymer with hydration sites which is compatiblewith the remainder of the ingredients of the diffusion matrix to permitthe sustained release of a drug, the balance being water. This watersoluble polymer complements the polyvinylalcohol by providing retentionof shape of the desired diffusion matrix. As such water soluble polymerwith hydration sites suitable for the present invention may be mentionedagar, agarose, polyvinylpyrrolidone and water soluble derivatives. Thematrix may further contain a therapeutically effective amount of one ormore drugs suitable for topical or transdermal application to a patient,thus forming a drug delivery device.

When the present polymeric diffusion matrix is used as a burn matrix,the matrix is preferably in a cured state. By cured, it is meant thatthe polymeric diffusion matrix contains little or no excess water usedin forming the matrix. As shown below, the diffusion matrix is formed bymixing together the glycerol, polyvinylalcohol, water soluble polymerwith hydration sites and water to obtain a homogeneous mixture which iscast into sheets of the matrix. In order to allow casting of themixture, it is sometimes necessary to use an excess amount of water.Immediately after casting, the polymeric matrix is in an "uncured"state. The excess water may then be permitted to evaporate. Whensubstantially all of the excess water has evaporated, the polymericmatrix is in a "cured" state. As a result of the evaporation of thewater, which generally requires from about 1 to about 18 hours, thethickness of the diffusion matrix is reduced, or a "collapsed" matrix isobtained.

In a first embodiment, the present invention provides a diffusion matrixfor the application of drugs to a patient (drug delivery matrix). Inanother aspect of the present invention, the transdermal or topicalapplication of drugs is contemplated via the diffusion matrix. Thediffusion matrix of the present invention provides a steady release ofthe drug to the patient over an extended period, typically 24 hours.

In its uncured state, the polymeric diffusion matrix comprises,preferably, from about 2 to about 20% glycerol, from about 2 to about15% polyvinylalcohol, from about 2 to about 10% polyvinylpyrrolidone,and the balance water, all percentages being by weight. Agar, agarose,water soluble cellulose derivatives or other compatible substances mayreplace all or part of the polyvinylpyrrolidone.

In the uncured matrix, the glycerol is present in an amount of fromabout 2 to 60%, preferably from about 2 to about 20%, by weight. Whentrinitroglycerol is the drug to be applied, the amount of glycerolpreferably should be within the range of from about 35 to 60%.Preferably, the glycerol has a minimum specific gravity of 1.23 g/ml.

The polyvinylalcohol is present in the uncured matrix in an amount offrom about 2 to about 15%, preferably from about 4 to about 9% byweight. Preferably, the polyvinylalcohol has a molecular weight of atleast about 70,000. Most preferably, the molecular weight is from about100,000 to about 150,000.

The water soluble polymer with hydration sites is present in the uncuredmatrix in am amount of from about 2 to about 10%, preferably from about2 to about 5%, by weight. In a preferred embodiment,polyvinylpyrrolidone is used as the water soluble polymer. The molecularweight for the polyvinylpyrrolidone should be selected to maintain watersolubility. In general, this molecular weight should be within the rangeof from about 20,000 to about 60,000, preferably from about 35,000 toabout 50,000. The polyvinylpyrrolidone may be replaced by otheringredients which permit sustained release. e.g. agar in an amount offrom about 2% to about 6% by weight may be used.

The balance of the matrix comprises essentially water.

In its cured state, the polymeric diffusion matrix comprises, from about2 to about 55%, preferably from about 4 to about 35% glycerol, fromabout 4 to about 30%, preferably from about 8 to about 20%polyvinylalcohol; from about 2 to about 20%, preferably from about 4 toabout 10% a water soluble polymer having hydration sites, preferablypolyvinylpyrrolidone, and the balance water, all percentages being byweight. The molecular weight ranges for the polyvinylalcohol andpolyvinylpyrrolidone are the same for cured and uncured diffusionmatrices. The cured matrix has a density of about 1.2 g/ml. It is notedthat the weight ratio of glycerol to water in the cured matrix is about0.6-1.8:1, preferably about 1:1. The cured matrix shows little swellingwhen immersed in water and will not dissolve in water at roomtemperature. However, if the water is heated to boiling, the diffusionmatrix will dissolve.

At least one drug is dispersed throughout the diffusion matrix when thediffusion matrix is used as a drug delivery device. The type of drugwhich may be dispersed in the diffusion matrix of the present inventionincludes any drug which is capable of being transdermally or topicallyadministered to a patient. With the sustained release of the drug at arelatively steady rate over a prolonged period, typically 24 hours, thepatient is provided with the benefit of a steady application of the drugover the prolonged period. As examples of drugs which are suitable forinclusion in the diffusion matrix of the present invention there may bementioned the following: alpha-[1(methylamino)ethyl1-benzene methanol,which is useful as an adrenergic (bronchodilator);N-phenyl-N-]1-(2-phenylethyl)-4-piperidinyll propanamide, useful as anarcotic analgesic;6-chloro-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-sulfonamide1,1-dioxide, useful as a diuretic;2-diphenylmethoxy-N,N-dimethylethanamine, useful as an antihistamine;and an estrogen. Other useful drugs include: anti-microbial agents suchas penicillin, tetracycline, oxytetracycline, chlortetracycline,chloramphenicol, and sulfonamides, sedatives and hypnotics such aspentabarbital sodium, phenobarbital, secobarbital sodium, codeine,(α-bromoisovaleryl) urea, carbromal, and sodium phenobarbital; psychicenergizers such as 3-(2-aminopropyl) indole acetate and 3-(2-aminobutyl) indole acetate; tranquilizers such as reserpine,chlorpromazine hydrochloride, and thiopropazate hydrochloride; hormonessuch as adrenocorticosteroids, for example, 6-methylprednisolone;androgenic steroids, for example, methyltestosterone, andfluoxymesterone; estrogenic steroids, for example, estrone, estradioland ethinyl estradiol; progestational steroids, for example,17α-hydroxyprogesterone acetate, medroxyprogesterone acetate,19-norprogesterone, and norethindrone; and thyroxine; antipyretics suchas aspirin, salicylamide, and sodium salicylate; morphine and othernarcotic analgesics; antidiabetics, e.g. insulin, antipasmodics such asatropine, methscopolamine bromide, methscopolamine bromide withphenobarbital; antimalarials such as the 4-aminoquinolines,9-aminoquinolines, and pyrimethamine; and nutritional agents such asvitamins, essential amino acids, and essential fats. The above listingof drugs is merely exemplary of the transdermally applicable drugs. Itis contemplated that any drug which may be transdermally applied issutiable for use as the drug to be applied via the diffusion matrix inthe present device.

It will be appreciated that the drug may be added to the above mixturenot only in the form of the pure chemical compound, but also inadmixture with other drugs which may be transdermally applied or withother ingredients which are not incompatible with the desired objectiveof transdermally administering the drug to a patient. Thus, simplepharmacologically acceptable derivatives of the drugs such as ethers,esters, amides, acetals, salts, and the like may be used. In some casessuch derivatives may actually be preferred.

The amount of the drug dispersed in the diffusion matrix can be variedin accordance with the desired dosage and the length of time the matrixis to remain on the skin. However, the amount of the drug included inthe matrix should generally be in excess of the amount which is to bedelivered to the patient. If the diffusion matrix is to be used for 24hours, an approximate 10 fold excess of the drug should be included. Forexample, if it is desired to apply about 5 mg of trinitroglycerol to apatient over 24 hours, a roughly ten fold excess of the trinitroglycerolshould be included in the diffusion matrix. Accordingly, from 40 to 60mg is considered a preferred amount to provide a 5 mg release oftrinitroglycerol over a 24 hour period. Quite obviously, the optimumamount that should be included in the diffusion matrix will varyaccording to factors such as the period of release of the drug.

In a preferred embodiment, there is used trinitroglycerol or1,2,3-propanetriol trinitrate or nitroglycerin, which is useful incoronary medicine as a vasodilator. It is preferred to add thetrinitroglycerol in the form of lactose triturate, in view of the dangerof explosion of trinitroglycerol. In addition, the ratio of lactosetriturate to the water and glycerol should avoid proportions where thetrinitroglycerol may separated and raise and explosion hazard. Apreferred lactose triturate is a composition comprising 10%nitroglycerin and 90% beta-lactose.

In forming the trinitroglycerol-containing matrix, excess water is notrequired. Hence, this matrix comprises from about 35 to about 60%,preferably from about 45 to about 55% glycerol; from about 2 to about15%, preferably from about 4 to about 9% polyvinyalcohol; from about 2to about 10%, preferably from about 2 to about 5% polyvinylpyrrolidone,and the balance being essentially water, all percentages being byweight. The amount of water evaporated from the uncured matrix isnegligible, hence, the higher percentage for the glycerol. For thismatrix, the weight ratio of glycerol to total polymers is usuallygreater than 1, preferably from about 1.4 to 15:1.

The amount of trinitroglycerol which should be used is based upon adesired delivery of about 5 mg per patient over a 24 hour period. Thediffusion matrix drug delivery system of the present invention todeliver the 5 mg in the 24 hour period should contain about 40 to 60 mgof the trinitroglycerol. To reach this objective, the concentration ofthe trinitroglycerol in the diffusion matrix and the area of thediffusion matrix are factors to consider. In accordance with a preferredaspect of the present invention, from about 0.1 to about 4.0% by weighttrinitroglycerol is included in the diffusion matrix. In a preferredaspect of the present invention, 80 ml of the solution is mixed with 20gm of lactose triturate, with this mixture being mechanically stirreduntil it is homogenous. The resultant homogenous mixture is poured intoforms preferably made of glass or stainless steel, these forms ortemplates producing a diffusion matrix having a thickness of about 3 toabout 4 mm, in accordance with a preferred aspect of the presentinvention. This diffusion matrix is either cast or cut into pieces ofthe desired size. In a preferred aspect, squares of about one inch oneach side, or about 6.5 cm² , have been prepared or ease of applicationto the patient.

The following methods may be used for preparing the diffusion matrix ofthe present invention.

In a first method, the matrix is formed at atmospheric pressure. Waterand glycerol are first mixed togethe. Since alkaline mixtures haverelatively poor stability, the pH of the mixture is adjusted so that itis either neutral or slightly acidic, i.c., the pH ranging from about6.5 to about 7.0. In a preferred embodiment, the pH is adjusted towithin the above-mentioned range by adding sodium citrate and citricacid to the mixture.

The polyvinylalcohol an polyvinylpyrolidone are then added to theglycerol-water mixture at room temperature, with agitation. The mixtureis heated to a temperature within the range of from about 90 to about95° C. at atmospheric pressure to extend the polymers. The mixture isheld at this temperature for about one hour. If desired, the mixture maybe maintained at this temperature for a period of about 48 hours priorto the addition of the drug. Thus, the mixture is stable for a period ofabout 48 hours and may be kept for such a period before being mixed withthe drug to be delivered to the patient. Thereafter, the mixture iscooled to 80° C. and stirred for an additional hour to remove bubblestherefrom. The drug to be applied to the patient is then added to themixture, with thorough agitation. Once a homogenous mixture of thepolymer solution and drug is obtained, the mixture is ready to be castinto sheets of the drug-containing diffusion matrix. In a preferredembodiment, the drug may be dissolved by agitation in a suitable solventsuch as glycerin and water. The thus-obtained solution can be maintainedat room temperature for prolonged periods without deterioration.

In a second method, water and glycerol are mixed, with the pH of themixture adjusted to a desired value by adding suitable amounts of sodiumcitrate and citric acid. Thereafter, the polyvinylalcohol andpolyvinylpyrolidone are added. The resulting mixture is then heated to atemperature of about 120° C. at a pressure of about 2 atmospheresabsolute. The temperature is maintained for about 1 hour without anymechanical agitation. In a preferred embodiment, the heating may beperformed in an autoclave. Since bubbles are not formed when the heatingis conducted in an autoclave, such a procedure is preferred. Thereafter,the temperature is lowered to about 20 to about 80° C. whereupon thedrug to be applied to the patient is added. After the drug has beenhomogenously dispersed in the liquid mixture, the mixture is poured intomolds to form sheets of the drug-containing diffusion matrix.

In the above methods and for the case of trinitroglycerol and otherdrugs having similar limitations, the drug must be added and mixedthoroughly when the polymer mixture is in the liquid state. Furthermore,the mixture should be cast within about 30 minutes after the drug hasbeen introduced into the polymer solution. This is important in order toavoid the setting of the polymer solution prior to casting.

The temperature at which the drug is to be added to the matrix solutiondepends on the stability of the drug. For example, trinitroglycerolbegins to decompose at a temperature of above about 50° C. Accordingly,in preparing a trinitroglycerol-containing diffusion matrix, the matrixsolution mixture is cooled to about 50°C., whereupon thetrinitroglycerol is added. The drug-containing diffusion solution isthen cast into molds to form sheets of the final product. In addition,for trinitroglycerol, the pH of the solution mixture should be keptslightly acidic, i.e., between 6.5 and 7.0 since trinitroglycerol isstabilized within this pH range.

A hydrophobic coating on a drug delivery matrix may be desired in thecase of treating patients having wounds or burns. Silicone oil may beadded in amounts of about 0.1 to 10% weight, based on the matrix, in theinitial mixture of glycerol and water. Mineral oil or vegetable oil maysubstitute in whole or in part for the silicone oil. The oil serves tolower transdermal loss of water in the wounded or burned patient.

Dodecyl alcohol or sorbitan (Tween-20) or other detergents may be addedin an amount of 0.1 to 10% by weight, based on the matrix, as adispersing agent, if desired.

For drugs that are alcohol-soluble, it may be desirable to add theinitial mixture of glycerol and water, ethanol or isopropanol in anamount of from 2 to 40% by weight, based on the matrix, to facilitatethe preparation of a diffusion matrix for such alcohol-soluble drugs. Inaddition, ethanol and isopropanol, when added to the initial mixture,will provide a "collapsed" diffusion matrix, i.e., as the ethanol andisopropanol evaporate the diffusion matrix produced in accordance withthe present invention will "collapse".

An absorption facilitator to insure skin penetration such asdimethylsulfoxide, decylmethylsulfoxide, or other penetration enhancersmay be added.

If it is desired to increase the effective lifetime of the diffusionmatrix, a drug reservoir may also be attached to the diffusion matrix.The diffusion matrix may also be used to help with local vasodilation toassist in the solution of physiological problems resulting from localcirculatory difficiencies, for example, to promote circulation in theextremities of a geriatric patient.

The present drug delivery device comprises the drug-containing diffusionmatrix and means for fastening the matrix to the skin of a patient. Suchmeans can take various forms, such as an occlusive backing layer forminga kind of "bandage" with the diffusion matrix being held against theskin of a patient being treated. A polyethylene or Mylar tape iscontemplated as one form of occlusive layer in accordance with thepresent invention. It can also take the form of an elastic band, such asa cloth band, a rubbery band or other material. Here, the diffusionmatrix is placed directly on the skin and held in place by such elasticband which typically will be placed over the arm or wrist of thepatient. An intermediate adhesive layer between the diffusion matrix andthe skin capable of permitting the transdermal application of the drugcan also be used.

As a preferred embodiment in the packaging of the present matrix, thedrug-containing diffusion matrix is placed in a cavity provided in aninert backing material. Useful backing materials include metal foilssuch as aluminum foil, polyolefins such as polyethylene andpolypropylene, polyesters such as Mylar (polyethylene terephthalate),polyamides such as Nylon, and the like. The drug-containing diffusionmatrix can be poured in its molten state into the cavity and permittedto cool. An adhesive layer is provided on the backing materialsurrounding the cavity. To prevent air from coming into contact with thematrix, the adhesive layer and the matrix are sealed with a releaselayer. To use the device, the patient peels off the release layer andplaces the device in intimate contact with his skin. The exposedadhesive layer secures the device to the patient. Since a concentrationgradient exists in a plane normal to the surface of the matrix and thepatient's skin, this condition facilitates the drug to diffuse throughthe matrix into the patient's body. Thus, there is provided a devicewhereby a drug is delivered transdermally to a patient at a steady rateover a prolonged period of time.

The contruction of a preferred embodiment for the packaging of thepresent invention is shown in further detail in FIGS. 1 and 2. Asillustrated in the Figures, the package comprises a bandage having coverlayer 12 and backing member 10. The diffusion matrix 14 having a drug(e.g. trinitroglycerol) dispersed therein is placed in cavity 16 inbacking member 10. This diffusion matrix may be poured in its moltenstate into cavity 16 in backing member 10 and permitted to cure.Alternatively, the molten polymeric mixture (with or without a drug) iscast to form a thin sheet which is cut, after curing, into smallersheets to fit the particular application of the matrix. Individualsmaller sheats may then be placed in cavity 16 in backing member 10. Thearea 18 surrounding the matrix in the backing member 10 is heat sealedto prevent the matrix from being removed from the backing member. Thebacking member 10 is formed of a laminate comprising an outer layer 20made of a polyester, such as polyethylene terephthalate, an intermediatelayer 22 made of a metallic foil, e.g. aluminum foil, and an inner layer24 made of a ionomer, such as Surlyn. A layer of pressure sensitiveadhesive 26 is provided on the surface of the inner layer surroundingthe heat sealed portion. It is noted that the adhesive does not coverthe matrix.

The matrix is prevented from coming into contact with the atmosphere byplacing cover layer 12 thereon, which seals the matrix. The cover layeris also formed of a laminate having the same construction as the backinglayer, i.e. an outer layer 28 made of a polyester, e.g. polyethyleneterephthalate; an intermediate layer 30 made of a metallic foil, e.g.aluminum foil; and an inner layer 32 of an ionomer, e.g. Surlyn. Thesurface of the inner layer coming into contact with the pressuresensitive adhesive 26 on the backing member 10 is coated with a releaselayer to permit easy removal of the cover layer.

To apply the drug to the patient, the cover layer is peeled off. Theexposed matrix is then taped onto a suitable portion of the patient'sbody, e.g. arm or wrist, to allow the drug to diffuse thereinto.

In the preferred embodiment wherein trinitroglycerol is dispersed in thepolymeric diffusion matrix, the molton matrix is cast into cavitiesprovided in the backing member. The matrix is permitted to cure for ashort period (e.g. about 10 minutes to about one hour) and is sealed byplacing the cover layer over the backing member.

In another embodiment of the present invention, a polymeric matrix forapplication to a burned portion of a patient's body is provided (burnmatrix). In this embodiment, the matrix comprises a water solublepolymer with hydration sites, polyvinylalcohol, glycerol and water.Examples of the water soluble polymer include polyvinylpyrrolidone,agar, agarose, water-soluble cellulose derivatives, and other compoundswhich are compatible with the remainder of the ingredients of thediffusion matrix of the invention to permit sustained release of a drug.

For a matrix in an uncured state, the water soluble polymer is presentin an amount of from about 2 to about 10%, preferably from about 3 toabout 8% by weight. For polyvinylpyrrolidone, which is a preferred watersoluble polymer, it has a molecular weight of from about 25,000 to about60,000, preferably from about 35,000 to about 50,000. Thepolyvinylalcohol is present in an amount of from about 2 to about 15%,preferably from about 6 to about 12% by weight. The polyvinylalcohol hasa molecular weight of from about 100,000 to about 150,000, preferablyfrom about 120,000 to about 135,000. The glycerol is present in anamount of from about 2 to about 20%, preferably from about 2 to about18% by weight. Preferably, the glycerol is a 96% aqueous glycerolsolution.

As a preferred embodiment, there is provided a polymeric diffusionmatrix which comprises in its uncured state and on a weight basis: about10.5% polyvinylalcohol (molecular weight 126,000); about 6%polyvinylpyrrolidone (molecular weight 40,000); about 15% glycerol; andthe balance water.

The relative weight amounts of polyvinylalcohol to polyvinylpyrrolidonethat have been considered range from about 3:1 to about 1:1. In actualpractice, however, at a range of about 3:1, less than optimum resultsare obtained with the burn matrix swelling to an unacceptable degree,and at the ratio of 1:1 the burn matrix tends toward being soft andsticky Accordingly, in accordance with a preferred aspect of the presentinvention, it has been discovered that a weight range ofpolyvinylalcohol to polyvinylpyrrolidone should be between about 2:1 andabout 3:2. The weight ratio of glycerol to total polymers for the burnmatrix is usually less than 1, preferably about 0.5-1:1.

The amount of water which is to be utilized in the preparation of a burnmatrix in accordance with the present invention in its generic aspect isrelated to the amount of glycerol which is used to make the burn matrixof the present invention. The amount of water by volume exceeds theamount of glycerol that is used in the initial mixture of ingredients.According to a preferred embodiment of the present invention, water ispresent in an amount of from about three to about seven times the amountof glycerol present in the initial mixture of ingredients. After themanufacture of the burn matrix of the present invention, the matrix is"cured" to eliminate most of the water, where water has been used inexcess. The amount of time for the cure depends upon conditions such asthe amount of excess water. In a preferred embodiment where 20 ml ofglycerol is mixed with 100 ml water, the cure time is about 24 hours,yielding a burn matrix with an approximately equal amount of water andglycerol.

In order to prepare the burn matrix of the present invention, the waterand glycerol are mixed together, preferably at a somewhat elevatedtemperature, e.g., 50° C. The polyvinylalcohol and thepolyvinylpyrrolidone are added under agitation with the temperaturebeing raised and with continued agitation until solution is effected.The temperature in one embodiment is raised to about 95° C. withsolution being effected at that temperature. The resultant homogenousmixture is then poured onto forms which are typically of glass orstainless steel serving as templates to produce a burn matrix having athickness of about 3 to about 4 mm. Where exccess water has beenincluded in the burn matrix, the burn matrix is cured to permitelimination of the excess water. For example, where a 5:1 volume ratioof water to glycerol is used, the freshly prepared burn matrix ispermitted to set for about 24 hours, resulting in a burn matrix having athickness of about 1 to 2 mm. The preferred thickness for a "cured" burnmatrix is from about 0.1 to about 2 mm.

The molten burn matrix is preferably cast to form a sheet of the matrix.After curing, the sheet is cut into smaller sheets having a suitablesurface area. The smaller sheets can then be deposited on an appropriatebacking layer. Alternatively, the molten burn matrix material can bepoured onto a backing layer to form a sheet of the matrix in intimatecontact with the backing layer. The backing layer can be made oflaminates comprising a polyester outer layer, a metal foil intermediatelayer, and a ionomer inner layer. The matrix/backing layer laminate canbe wound to form a roll of the matrix or cut into smaller sheets ofsuitable size.

Where drugs are to be included in the burn matrix, they may be added, inthe case of drugs soluble in the burn matrix, to the homogenous mixtureprior to casting, or after curing of the matrix, by the physician orpharmacist at his direction shortly before the need for applicationarises, permitting a wider flexibility in topically applying a medicineto the patient. Generally, water insoluble drugs may be included in theburn matrix either through original incorporation into the mixture ofwater and glycerol or through subsequent application of the drug intothe already prepared burn matrix. Where the drug is to be applied to atypical burn matrix of the invention having a thickness of about 2 mm,the drug may be painted onto a surface of the burn matrix or it may beapplied through other means, such as an aerosol. A sufficient period oftime, e.g., 4 hours, should be provided for the drug to diffuse throughthe burn matrix of the present invention. In order to provide ananesthetic effect, a water soluble anesthetic such as xylocaine may beapplied through any of the above modes available for water solubledrugs. The amount of the water soluble drug that is to be dispersed inthe burn matrix of the present invention should be in excess of theamount which is to be administered to the patient. An excess of 1:1 to10 times the actual amount of drug which is to be administered to thepatient should generally be used.

A water-soluble antibiotic to counter the possibility of infectionshould also be considered for inclusion in the burn matrix of thepresent invention. Because of the option of including the specificallydesired antibiotic after the preparation of the burn matrix of thepresent invention, the individual physician is given great latitude inselecting the desired antiobiotic to take into account the particularneeds of the specific patient being treated. As an example of a watersoluble antibiotic which may be incorporated into the burn matrix of thepresent invention may be mentioned Penicillin VK.

Water insoluble materials may also be desirably included in the burnmatrix of the present invention. Such materials are preferablyintroduced directly into the initial mixture of water and glycerol atthe outset of the manufacturing process for making the burn matrix ofthe present invention. In accordance with one aspect of the invention,there is provided a zinc substance in an amount from about 0.4 to about2% by weight based upon the final weight of the cured burn matrix of thepresent invention. Zinc chelates may be used as the zinc substance ofthis aspect of the present invention. In accordance with a furtherembodiment within the scope of the present invention about 0.4 to about2% by weight zinc or silver sulfadiazine is incorporated into the burnmatrix of the present invention for retarding Pseudomonas infections.

In making zinc or silver (or other water-insoluble containing) burnmatrix of the present invention, the zinc or silver material ispreferably added with a small amount of the glycerol. The amount ofglycerol needed to make the suspension is subtracted from the amount ofglycerol initially mixed with the water. A uniform suspension of thezinc or silver compound and glycerol is added together with the waterand remainder of the glycerol, preferably as the last stage prior tocasting.

In addition to local anesthetics and antibiotics which can be applied toor incorporated into the burn matrix of the present invention, othertopical medicines may also be applied to or incorporated in the burnmatrix. Examples of useful topical drugs include fungicides,bactericides, antimicoplasma (E. coliplasma), analgesics and localanesthetics.

The amount of drug which can be incorporated into the burn matrix is upto about 1% by weight of the burn matrix. By incorporated, it is meantthat the drug is added to the polymer mixture before casting. As to theamount of drug which can be painted onto the suface of the matrix thisvaries in accordance with the drug applied.

If desired, a hydrophobic casting may be desired in the burn matrix ofthe present invention. Silicone oil may be added in amounts of about 0.1to 10% by weight, based on the matrix in the initial mixture of glyceroland water. Mineral oil or vegetable oil may substitute in part or wholefor the silicone oil, which lowers the transdermal loss of water in thepatient.

The burn matrix in accordance with the present invention is a flexibleand transparent polymer which is suited for being applied directly to aburned portion of the patient being treated for most parts of the body.After hydration, the burn matrix is highly flexible and will adheremildly to the skin. The degree of adherence is sufficient to hold theburn matrix in place but not enough to injure the patient's skin when itis removed. It is contemplated that the burn matrix should be replacedperiodically, typically at 24 hour or longer intervals.

The burn matrix of the present invention may be stored for prolongedperiods, particularly when placed in a sealed container.

The cured matrix of the present invention can be used in agriculturalapplications. In such instances, pesticides (for controlling microbialand other disease causing organisms), herbicides, insecticides andinsect repellents may be incorporated in the matrix. The matrix can beapplied to the animal or plant topically or parenterally (i.e. byimplantation).

The method of administration of this invention is suitable also foradaptation to buccal and especially to sublingual administration.Because of the much higher rate of absorption through the mucosa by thatroute, much shorter periods of administration are required.

The invention is illustrated by the following nonlimiting Examples:

EXAMPLE I

45 ml glycerol and 45 ml water together with 1% by weight sodium citrateare mixed together and the pH adjusted to 7 through addition of citricacid. This mixture is heated to 90° C.; after reaching at least 70° C.there are slowly added 7 gm polyvinyl alcohol (PVA 100% hydrolyzed,molecular weight 115,000) and 5 gm polyvinylpyrrolidone (mw 40,000). Themixture is stirred at 90° C. until solution is effected, which may takeabout 10 minutes, it being appreciated that with larger quantities, aconsiderably longer period of time may be needed. 80 ml of this solutionis then mixed with 20 gm lactose triturate (10% nitroglycerin and 90%lactose), this mixture then being mechanically stirred until homogenous.The homogenous mixture is then poured into forms made of glass orstainless steel which serve as templates to produce a diffusion matrixhaving a thickness of about 3 to 4 mm. This diffusion matrix is then cutinto square pieces of about 1 inch on each side, i.e., to provide atotal surface area of about 6.5 cm².

EXAMPLE II

Example I is repeated with the exception that 3 gm of agar is usedinstead of the polyvinylpyrrolidone. Also included in the mixture is 1%by weight calcium chloride.

EXAMPLE III

The diffusion matrix of Example I is applied to a patient by placing itagainst the wrist, shoulder or other sites of the patient.

EXAMPLE IV

The diffusion matrix of Example I is applied to a patient by firstattaching the diffusion matrix to a MYLAR or polyechylene backing layer.This occlusive backing layer is provided with an adhesive whereby thediffusion matrix is held in contact with the skin as part of this"bandage".

EXAMPLE V-X

By substituting an appropriate amount of the following chemicals, inplace of the lactose triturate, otherwise following the procedure ofExample I, a diffusion matrix is obtained:

    ______________________________________                                        EX-                                                                           AMPLE  COMPOUND             USE                                               ______________________________________                                        V      Alpha-[1(methylamino)-ethyl]                                                                       adrenergic                                               benzene methanol     (bronchodilator)                                  VI     N--phenyl-N--[1-(2-phenylethyl)-                                                                   narcotic analgesic                                       4-piperidinyl]propamide                                                VII    6-chloro-3,4-dihydro-2H,1,2,4-                                                                     diuretic                                                 benzothiadiazine-7-sulfonamide                                                1,1-dioxide                                                            VIII   2-diphenylmethoxy-N,N--dimethyl-                                                                   antihistamine                                            ethanamine                                                             IX     estra-1,3,5(10)triene-3-,17beta-                                                                   estrogenic                                               diol                                                                   X      5-ethyl-5-phenyl-2,4,6(1H,3H,5H)-                                                                  anticonvulsant,                                          pyrimidinetrione     hypnotic, sedative                                ______________________________________                                    

EXAMPLE XI

948 g of 96% glycerol and 644 g of water are mixed together. 27 g ofsodium citrate, 159 g of polyvinyl alcohol (molecular weight 115,000),93 g of polyvinylpyrrolidone (molecular weight 40,000) are dissolved inthe glycerol/water mixture by continuous stirring and maintaining at atemperature of about 90° C.

In a separate container, 600 g of nitroglycerin triturate (10%nitroglycerin and 90% lactose) is dissolved in 315 g glycerol and 214 gwater with agitation at room temperature.

When the polymers have gone into solution, the nitroglycerin trituratedispersion is poured therein. The mixture is mixed thoroughly at atemperature range of between 50° and 55° C. to form a homogenousmixture. The container is kept covered.

The homogenous mixture is poured into forms made of glass or stainlesssteel which serve as templates to produce a drug-containing diffusionmatrix having a thickness of about 3 to 4 mm. This diffusion matrix isthen cut into square pieces of about 1 inch on each side, i.e. toprovide a total surface area of about 6.5 cm².

EXAMPLE XII

100 ml and 20 ml glycerol are mixed together and heated to about 50° C.8 gm polyvinylalcohol (molecular weight 126,000, 100% hydrolyzed) isslowly added while the preparation is undergoing rapid agitation. Afterthe polyvinylalcohol is uniformly dispersed, 5 gm polyvinylpyrrolidone(molecular weight 40,000) is added with continued stirring. Thepreparation is then heated to about 95° C. until solution is effected.At this point, the preparation may be cast onto a flat sheet so that itcan harden.

The homogenous mixture is poured onto a stainless steel plate resultingin an uncured burn matrix having a thickness of about 3 to 4 mm. Theburn matrix is cured by letting water evaporate for about 24 hours,leaving a cured burn matrix having a thickness of about 1 to about 2 mm.

The burn matrix has the following compositions:

    ______________________________________                                                         % by weight                                                  Ingredients        uncured  cured                                             ______________________________________                                        glycerol           17.9     34.6                                              polyvinylalcohol   5.8      11.3                                              polyvinylpyrrolidone                                                                             3.6      7.0                                               water              72.7     47.0                                              ______________________________________                                    

EXAMPLE XIII

A piece of the cured burn matrix of Example XII is placed on a testsystem of 10% aqueous gelatin cast into a petri plate, to serve as amodel for testing the burn matrix. On this model, it was found that theburn matrix of the present invention does not appreciably swell but doespermit a small amount of water evaporation and further permits theexchange of some gases by diffusion processes across the perpendiculardimension of the burn matrix. The burn matrix of the present inventionretards the loss of water vapor from a 10% gelatin preparation byapproximately a factor of 10.

EXAMPLE XIV

A one inch square piece of the cured burn matrix of Example XII is usedas a model for preparing a burn matrix with water soluble medicinaladditives. Painted onto one side of the burn matrix of Example I is 10mg of Xylocaine. After painting the Xyocaine onto the burn matrix, theburn matrix is permitted to stand for about 4 hours, resulting in a burnmatrix having diffused therein the Xylocaine.

EXAMPLE XV

In place of the Xylocaine of Example XIV, 30 mg of Penicillin VK isapplied to the burn matrix, resulting in a burn matrix having antibioticproperties over the 24 hour period desired for the life of the burnmatrix.

EXAMPLE XVI

Example XIV is repeated, except that in addition to the Xylocaine, thereis also simultaneously painted onto the burn matrix 30 mg Penicillin VK.The resultant burn matrix provides both antibiotic protection againstinfection and relief from pain over an extended period, due to the slowrelease of the Xylocaine over a prolonged period.

EXAMPLE XVII

The procedure of Example XII is repeated, with the following variations:18 ml instead of 20 ml glycerol is used. In addition, sufficient zincsulfadiazine to make up 1% by weight of the final cured burn matrix issuspended in 2 ml glycerol. This suspension is added to the mixture ofother ingredients as the last step prior to pouring onto the stainlesssteel plate.

The resultant cured burn matrix provides the additional advantage ofprotecting the burn victim over an extended period against Pseudomonasinfection. In place of zinc sulfadiazine, silver sulfadiazine may beused.

EXAMPLE XVIII

The procedure of Example XVII is repeated except that the zincsulfadiazine is replaced by 20 mg of Cephalosporin, resulting in a burnmatrix having antibiotic properties.

EXAMPLE XIX

Male dogs are anesthetized with sodium pentothal. Through surgicalincisions, catheters are positioned in the femoral veins of each hindleg and in the abdominal aorta. Flow gauges are placed on the internaliliacs of both hind limbs. On a well-shaved area of the medial surfaceof the left thigh, a nitroglycerin containing polymer matrix obtained inExample I is taped in place and remains undisturbed for 4 hours. Theright hind limb receives no matrix or treatment of any kind. Afterapplication of the matrix, blood samples (5 ml) are taken from thecatheters in each of the femoral veins and from that in the abdominalaorta at 15, 30, 60, 120, 180 and 240 minutes. Once drawn, the bloodsamples are put in ice, centrifuged (for 10 minutes) at 0° C., and 2 mlplasma is transferred to a silanized (with an alkylated silicone oil)glass tube. To each tube, 5 ml n-pentane is also added and thenitroglycerin is extracted for 1 hour with gentle shaking at 0° C. Thepentane phase is then transferred to a 5 ml capacity Recti-Vial^(TM) andevaporated to near dryness. The residue is then dissolved in 30microliters benzene containing 2 nanograms para-nitro-anisole used asthe external standard. 1.0 to 50.0 microliters of this solution is theninjected for nitroglycerin quantitation using GLC-Electron CaptureDetection. (A Hewlett-Packard 4610A Gas chromatograph equipped with a ⁶³Ni-electron capture detector.) Separation is achieved on a 4 foot × 3 mmI.D. glass column packed with 10% SE-30 on 100/120 mesh GASCHROM Q^(TM).The column is maintained at 140° C. while the injection-port temperatureis 170° C. and detector temperature: 220° C. A nitroglycerin calibrationcurve is constructed from the analyses of nitroglycerin spiked blank-plasma.

The results from the above test runs, summarized in Table 1, showdramatically that nitroglycerin is absorbed transepidermally from thematrix over the entire 4 hour period. Also, the levels attained in thevenous blood draining the limb containing the matrix are grosslyproportional to the matrix surface area in contact with the skin.

From the results of the studies here discussed, it is evident thattransepidermal nitroglycerin absorption has occurred from the matrix toblood.

The nitroglycerin absorption rate appears to be fairly constant from30-240 minutes as depicted by the essentially non-varying arterialnitroglycerin plasma levels.

                  TABLE I                                                         ______________________________________                                        MATRIX SIZE -                                                                              2" × 3"                                                                            2" × 1"                                                                           1" × 1"                               STUDY No.    1          2         3                                           SAMPLE       nanograms nitroglycerin per ml. plasma                           ______________________________________                                        ARTERIAL - 15 min.                                                                         0.68       0.14      0.27                                        ARTERIAL - 30 min.                                                                         0.57       0.15      0.53                                        ARTERIAL - 60 min.                                                                         0.73       0.15      --                                          ARTERIAL - 120 min.                                                                        0.85       0.49      0.36                                        ARTERIAL - 180 min.                                                                        1.29       0.68      0.50                                        ARTERIAL - 240 min.                                                                        1.26       0.21      0.30                                        EXPERIMENTAL 0.95       5.70      0.40                                        VENOUS - 15 min.                                                              EXPERIMENTAL 0.51       8.31      0.32                                        VENOUS - 30 min.                                                              EXPERIMENTAL 15.3       11.4      0.52                                        VENOUS - 60 min.                                                              EXPERIMENTAL 26.9       7.63      0.75                                        VENOUS - 120 min.                                                             EXPERIMENTAL 32.9       13.7      0.57                                        VENOUS - 180 min.                                                             EXPERIMENTAL 32.0       5.55      0.23                                        VENOUS - 240 min.                                                             CONTROL      0.44       9.18      0.09                                        VENOUS - 15 min.                                                              CONTROL      0.61       21.6      0.15                                        VENOUS - 30 min.                                                              CONTROL      7.40       4.51      0.28                                        VENOUS - 60 min.                                                              CONTROL      2.33       13.0      0.42                                        VENOUS - 120 min.                                                             CONTROL      9.87       14.5      0.39                                        VENOUS - 180 min.                                                             CONTROL      13.9       4.10      0.23                                        VENOUS - 240 min.                                                             ______________________________________                                    

EXAMPLE XX

Five male mongrel dogs, free of disease, are anesthetized with sodiumpentobarbital. Under a septic surgical procedure, a catheter is insertedinto the right artrium via the jugular vein for the removal of bloodsamples from the right heart. An arterial catheter is placed in theright carotid artery for the continuous recording of arterial bloodpressure. Both catheters are exteriorized at the back of the neck.

The animals are allowed to recover from the anesthetic and are studied24 hours later in the fasted, conscious state while resting comfortablyin a supporting harness.

Each animal is allowed to become familiar with the laboratorysurroundings and when completely acclimated, a 20 ml reference bloodsample is obtained from the right heart catheter. A 1.0"×1.0" square ofthe nitroglycerin containing polymer matrix obtained in Example I isthen applied to a well shaved area of the right lateral chest wall. Thematrix is held securely in place with surgical tape. After applicationof the polymer matrix, 5.0 ml blood samples are obtained at 15 min, 30min, 45 min, 1 hr, 2 hr, 3 hr, 4 hr, 5 hr, 6 hr, 7 hr, 8 hr, 9 hr, 10hr, 11 hr, 12 hr, 14 hr, 16 hr, 18 hr, 20 hr, 22 hr and 24 hr. Theanimals are conscious and unrestrained during the entire 24 hour periodof sampling. At no time do the animals display any unfavorable effectsdue to the transcutaneous administration of nitroglycerin.

Immediately after drawing, blood samples are put in ice and transferredto a walk-in refrigerator and centrifuged for 10 minutes at 0° C. A 2 mlaliquot of plasma is taken from each specimen and transferred toindividual silanized (with an alkylated silicon oil) glass tubes. A 5 mlvolume of n-pentane is added to each tube and the nitroglycerin isextracted for 60 minutes with gentle shaking at 0° C. The pentane phaseis transferred to a 5 ml capacity Reacti-Vial and evaporated to neardryness. The residue is dissolved in 30 microliters of benzenecontaining 2 nanograms of para-nitro-anisole used as the externalstandard. A 1.0 to 5.0 microliter aliquot of this solution is injectedfor nitroglycerin quantitation using GLC-Electr 1 Capture Detection(Hewlett-Packard 4610A Gas Chromatograph equipped with a ⁶³ Ni-electroncapture detector.) Separation is achieved on a 4 foot × 3 mm I.D. glasscolumn packed with 10% SE-30 on 100/120 mesh GAS-CHROM Q^(TM). Thecolumn is maintained at 140° C. While the injection-port temperature is170° C., and detector temperature 220° C. A nitroglycerin calibrationcurve is constructed from the analyses of nitroglycerin-spiked blankplasma.

Table 2 summarizes the plasma nitroglycerin data from the dogs. At eachtime point the mean ± the standard deviation is listed in the Table.

                                      TABLE 2                                     __________________________________________________________________________    HOURS                                                                         POST     ng nitroglycerin/ml. plasma                                          APPLICATION                                                                            DOG #1                                                                             DOG #2                                                                             DOG #3                                                                             DOG #4                                                                             DOG #5                                                                             5 DOGS                                                                             +/- S.D.                               __________________________________________________________________________    0.25     0.11 0.39 --   0.37 --   0.29 0.16                                   0.50     0.08 0.28 0.02 0.16 0.16 0.14 0.098                                  0.75     0.08 0.29 0.02 0.14 0.19 0.14 0.10                                   1.00     0.23 0.19 0.15 0.10 0.36 0.21 0.099                                  2.00     0.22 0.57 0.02 0.22 0.27 0.26 0.20                                   3.00     2.06 0.38 0.04 0.88 0.17 0.71 0.82                                   4.00     0.52 0.81 0.11 0.28 0.26 0.40 0.27                                   5.00     0.22 1.00 0.28 0.17 0.11 0.36 0.37                                   6.00     0.23 0.63 0.24 0.55 0.88 0.51 0.28                                   7.00     0.93 0.70 0.45 0.34 1.23 0.73 0.36                                   8.00     0.16 2.39 0.70 0.42 0.45 0.82 0.90                                   9.00     0.22 0.59 0.32 0.34 0.10 0.31 0.18                                   10.00    0.11 0.83 0.59 0.31 0.66 0.50 0.29                                   11.00    0.07 0.77 0.13 0.35 0.50 0.36 0.28                                   12.00    0.35 0.55 0.37 0.29 0.12 0.34 0.15                                   14.00    0.04 0.39 0.18 0.17 0.20 0.20 0.13                                   16.00    0.07 0.41 0.28 0.57 0.32 0.38 0.17                                   18.00    0.26 1.17 0.32 0.29 0.39 0.49 0.39                                   20.00    0.34 0.41 0.52 0.33 0.24 0.31 0.11                                   22.00    0.20 1.11 0.66 --   --   0.66 0.46                                   24.00    0.27 0.43 --   --   --   0.35 0.11                                   __________________________________________________________________________

From these results, it is evident that transcutaneous nitroglycerinabsorption does occur, and does so at a constant and continuous rate soas to achieve a plateau plasma nitroglycerin level ranging from aboutaverage values of 0.3-0.6 nitroglycerin /ml. plasma. The data also showthat the temporal limits of the nitroglycerin matrix have not beenexceeded, or for that matter, have not been approached during the 24hour experimental period. In each case, the apparent plateaunitroglycerin level shows no evidence of decreasing, either before or atthe 24 hour experimental time limit.

What is claimed is:
 1. A transdermal drug delivery vehicle, whichcontains a sedative, chosen from the group consisting of pentabarbitalsodium, phenobarbital, secobarbital, sodium, codeine,(α-bromoisovaleryl)urea, carbromal and sodium phenobarbital, capable ofbeing delivered transdermally over a prolonged period of time throughthe unbroken skin of a patient, in the form of a shape-retaining matrixfor direct application to the skin of a patient in need of the sedativeto be delivered, said matrix comprising from about 2 to about 60%glycerol, from about 2 to about 15% polyvinylalcohol molecular weight offrom about 100,00 to about 150,000, from about 2 to about 10%polyvinylpyrrolidone molecular weight of from about 20,000 to about60,000 and the balance water, cast or molded from hot solution thereof.2. A transdermal drug delivery vehicle according to claim 1 incombination with an occlusive backing layer for holding the matrixagainst the skin of the patient being treated.
 3. A transdermal drugdelivery vehicle according to claim 1 wherein the matrix is placed in acavity in an inert backing material.
 4. A transdermal drug deliveryvehicle according to claim 1 wherein the matrix is molded in situ in thecavity.
 5. A transdermal drug delivery vehicle according to claim 1wherein the sedative is phenobarbital.
 6. A method of delivering asystemically active sedative to a patient over a prolonged period oftime at a steady rate which comprises applying to the skin of saidpatient a transdermal drug delivery vehicle, which contains a sedativecapable of being delivered transdermally over a prolonged period of timethrough the unbroken skin of a patient, said sedative chosen from thegroup consisting of pentabarbital sodium, phenobarbital, secobarbitalsodium, codeine, (α-bromoisovaleryl)urea, carbromal and sodiumphenobarbital, in the form of a shape-retaining matrix for directapplication to the skin of a patient in need of the sedative to bedelivered, said matrix comprising from about 2 to about 60% glycerol,from about 2 to about 15% polyvinyl alcohol molecular weight of fromabout 100,000 to about 150,000, from about 2 to about 10%polyvinylpyrrolidone molecular weight of from about 20,000 to about60,000 and the balance water, cast or molded from hot solution thereof.7. A method according to claim 6 wherein the transdermal drug deliveryvehicle is attached to an occulsive backing layer for holding the matrixagainst the skin of the patient being treated.
 8. A method according toclaim 6 wherein the matrix is located in a cavity in an inert backingmaterial.
 9. A method according to claim 6 wherein the sedative isphenobarbital.